dt-bindings: snps,dw-apb-ssi: add optional reset property

Add optional reset property.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Link: https://lore.kernel.org/r/20200529155806.16758-2-dinguyen@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>